The present invention relates to a semiconductor device, in the manufacturing process of which a trench is filled with an epitaxially grown film, and a method for manufacturing the device.
The inventors of the present invention propose the following method, which is shown in FIGS. 8A to 8F, for forming a trench in a semiconductor layer and filling the trench with an epitaxially grown film in U.S. Pat. No. 6,406,982 (JP-A-2002-124474). In the method, firstly, an n-type drift layer 120 is formed on an n+-type substrate 110 to form a semiconductor substrate 132, and a mask layer 131 is formed by patterning a film deposited on the substrate 132 using photolithography and etching, as shown in FIG. 8A.
Then, the n-type drift layer 120 is partially etched using the mask layer 131 in order to form trenches 111, as shown in FIG. 8B. Then, the mask layer 131 is removed using hydrofluoric acid (HF) aqueous solution, as shown in FIG. 8C. Next, the substrate 132 is heated in non-oxidizing and non-nitridizing atmosphere in order to smooth the surfaces of the trenches 111 and in order to cure the crystallographic defects located in the surfaces, as shown in FIG. 8D. After that, an epitaxially grown film 133 is deposited to fill the trenches 111, as shown in FIG. 8E. Finally, the epitaxially grown film 133 is planarized, as shown in FIG. 8F.
In the method of U.S. Pat. No. 6,406,982, as described, the substrate 132 is heated in the non-oxidizing and non-nitridizing atmosphere before the epitaxially grown film 133 is deposited. The heating enables the epitaxially grown film 133 to be deposited on the inner surfaces of the trenches 111, which has been smoothed and the crystallographic defects in which have been cured. As a result, the crystallographic defects that otherwise would be generated in the epitaxially grown film 133 are prevented.
However, there is a problem in the method of U.S. Pat. No. 6,406,982 that the dopant concentration in the substrate 132 can fluctuate to deviate from the predetermined concentration because the dopants contained in the semiconductor substrate 132 out diffuse during the heating.